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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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372                                 ALASKAN GLACIER STUDIES
by low tide water. On both sides of the lower part of the glacier is a distinct bare zone of smoothed granite, and t.hia bare zone, which is 100 to 500 feet in width, ends abruptly at the edge of a forest covered tract. This zone is prominently developed on a granite knob, almost an island, at the west side of the glacier front. Crossing the top of this knob is a small moraine . . . from 1 to 10 feet in height and 5 to 30 feet in width. This moraine contains decaying fragments of trees and just to the north of it is an area of scattering trees, some of which are a foot in diameter. To the south of the moraine is some vegetation,—moss, grass, alders 5 feet high, and a few spruce trees 4 feet high. Most ojf the vegetation disappears half way from the moraine to the ice front. From the extreme summit of the above granite knob the nearest point of the moraine is 48 feet distant in a direction S. 10° W. From the same summit the extreme front of the glacier is 500 feet distant in a direction S. 13° W.
*' The moraine noted above marks the farthest advance of the ice since the growth of the present forest, i. e., for a century, and most probably for a few centuries. The date of this maximum historical advance, is at a Ttiim'nniTn, twenty years, and probably the actual date is considerably longer ago than twenty years."
Two years later our comparison of photographs showed little retreat since 1908. The glacier surface was quite smooth and apparently still wasting, and a smaller portion of the ice front was bathed by low tide. The marginal stream on the eastern side was of great size and was building a steeply-sloping delta whose area increased greatly from 1908 to 1910. Grant's conclusion that the advance in association with the terminal moraine had taken place at least twenty years before 1908 would seem to associate the advance with the tidal condition of the glacier when mapped by Applegate in 1887. In connection with the long stand of the glacier terminus, with only about 500 feet of retreat in 38 years, there has accumulated an extensive terminal deposit of gravel, sand, and clay, laid down in large part below sea level. The weak terminal moraine on the land, the broader terminal deposit in the sea, and the barren zone are all conspicuous phenomena in connection with the history of Nellie Juan Glacier from 1887 to 1910.
The Ouiwash Fan. West of the rock hill a narrow lobe of the glacier sends a stream northward across an extensive outwash gravel fan, the margin of which is submerged for J mile at low tide. This fan, which is over £ mile wide, has tied Nichols Island to the mainland, but on the northern edge, near the island, there is a channel connecting the main cove with the narrow inlet to the west of Nichols Island. A slough of clear water flows across this flat even at low tide, and enters the bay in front of Nellie Juan Glacier. Its current is distinguishable for several hundred feet offshore in the midst of the milky-white glacial waters of the rest of the cove. Another of the streams from the western margin of the glacier flowed across the fan to the branch of the fiord west of Nichols Island. This portion of the fan completely surrounds a rock islet. The surface of the fan is barren, evidently because the glacial streams have occupied its surface continuously. It has an unusually steep slope and parts of it are made up of very coarse bowlders. In recent years, with the retreat of the glacier and diminution of debris supply, some of the streams have incised moderately-deep gulleys in the fan.
Ultramarine Glacier. This glacier terminates in Blue Fiord, which is 4$ miles long, ^ to 1 mile wide, and very precipitous. The length of the Ultramarine Glacier is unknown, only a mile of it having been mapped, and at the terminus it has a width of about £ of a mile (Fig. 55). Like Nellie Juan Glacier, it is fairly clean and moderately